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Makoto Tsubokura

Makoto Tsubokura
Kobe University/RIKEN · Graduate School of System Informatics/Center for Computational Science

PhD
Seeking for skilled post-doc. researchers: Development of HPC-CFD method, vehicle aero. or viral droplet simulations.

About

218
Publications
19,373
Reads
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1,030
Citations
Introduction
Research projects so far. Large Eddy Simulation (LES) for engineering applications. Applied Aerodynamics. High-Performance Computing (HPC) for turbulence simulation. HPC-LES for vehicle aerodynamics. K-computer for engineering applications.
Additional affiliations
April 2015 - present
Kobe University
Position
  • Professor (Full)
June 2012 - present
RIKEN
Position
  • Group Leader
Description
  • Dual affiliation with Kobe University
October 2007 - March 2015
Hokkaido University
Position
  • Professor (Associate)
Education
April 1994 - March 1997
The University of Tokyo
Field of study
  • Mechanical Engineering
April 1992 - March 1994
The University of Tokyo
Field of study
  • Mechanical Engineering
April 1988 - March 1994
Kyoto University
Field of study
  • Applied Physics

Publications

Publications (218)
Article
Full-text available
This numerical study reports the change in natural-convection heat transfer characteristics from a stationary 2D horizontal cylinder with the change in the aspect ratio (ratio of cylinder radius to enclosure length, \(R/L\)) of a cooled square outer enclosure and position of the cylinder for Rayleigh number \({(Ra}_{D})\) of \({1.114\times 10}^{4}\...
Article
In this study, the flow field around face masks was visualized and evaluated using computational fluid dynamics. The protective efficiency of face masks suppressing droplet infection owing to differences in the shape, medium, and doubling usage is predicted. Under the ongoing COVID-19 pandemic condition, many studies have been conducted to highligh...
Article
Full-text available
The physical variables involved in a flow field are of very different scales to those of the aeroacoustic field within the flow. Thus, direct aeroacoustic computations (DACs) require extremely small time steps to capture the fluctuations in the aeroacoustic field and stabilize the numerical scheme. As a result, the computation time for DACs can be...
Article
Vehicle aerodynamics and dynamics in gusty crosswind conditions are of increasing significance for the lateral stability of heavy ground vehicles, especially articulated heavy vehicles (AHVs). The unsteady aerodynamic loads acting on AHVs can greatly exceed loads of a single-vehicle unit; these may deteriorate the lateral stability and lead to a lo...
Preprint
Full-text available
In this study, the flow field around face masks was visualized and evaluated using computational fluid dynamics. The protective efficiency of face masks suppressing droplet infection owing to differences in the shape, medium, and doubling usage is predicted. Under the ongoing COVID-19 pandemic condition, many studies have been conducted to highligh...
Article
We propose a monolithic fluid–structure interaction (FSI) method that uses the cellcentered finite volume formulation in the Eulerian description, Lagrangian marker particles allocated in the solid region, and the incompressible mixture formulation. In the proposed method, we compute all the basic equations and spatial derivatives, except the solid...
Chapter
Nonlinear modes of the three-dimensional flow field around a cylinder were extracted by distributed learning on Fugaku. Mode decomposition is an approach used to decompose flow fields into physically important flow structures known as modes. In this study, convolutional neural network-based mode decomposition was applied to the three-dimensional fl...
Preprint
Full-text available
The fastest supercomputer in 2020, Fugaku, has not only achieved digital transformation of epidemiology in allowing end-to-end, detailed quantitative modeling of COVID-19 transmissions for the first time, but also transformed the behavior of the entire Japanese public through its detailed analysis of transmission risks in multitudes of societal sit...
Preprint
Full-text available
The dose-response model has been widely used for quantifying the risk of infection of airborne diseases like COVID-19. The model has been used in the room-average analysis of infection risk and analysis using passive scalars as a proxy for aerosol transport. However, it has not been employed for risk estimation in numerical simulations of droplet d...
Article
This paper presents a one-sided immersed boundary (IB) method using kernel functions constructed via a moving least squares (MLS) method. The resulting kernels effectively couple structural degrees of freedom to fluid variables on only one side of the fluid-structure interface. This reduces spurious feedback forcing and internal flows that are typi...
Article
Full-text available
The effects of the inclination angle of the incisor on the speech production of the fricative consonant /s/ was investigated using an implicit compressible flow solver. The hierarchical structure grid was applied to reduce the grid generation time for the vocal tract geometry. The airflow and sound during the pronunciation of /s/ were simulated usi...
Article
Full-text available
Natural convection in a three-dimensional square cavity with random artificial roughness on both vertical walls is studied numerically for a Rayleigh number of 10⁶. Based on consideration of realistic conditions, the roughness is generated using a given power spectrum density, and a compressible solver with preconditioning that uses a dual time-ste...
Article
To design a method to solve the issues of handling “dirty” and highly complex geometries, the topology-free method combined with the immersed boundary method is presented for viscous and incompressible flows at a high Reynolds number. The method simultaneously employs a ghost-cell technique and distributed forcing technique to impose the boundary c...
Article
In recent decades, growing efforts have been devoted to coupling the Computational Fluid Dynamics (CFD) and the Discrete Element Method (DEM), i.e., CFD-DEM coupling methods, to account for particle–fluid interactions. However, it remains a challenging task for the well-known Immersed Boundary Method (IBM) belonging to the resolved CFD-DEM methods...
Article
In this work, we propose a semi-implicit, density-based solver for compressible, evaporating particle-laden flow, and investigate its efficiency. It is established on a Cartesian-grid-based, scalable, numerical framework named CUBE. In this solver, the governing equation system is divided into three subsystems (compressible Navier-Stokes, species t...
Article
Full-text available
The effects of on-road disturbances on the aerodynamic drag are attracting attention in order to accurately evaluate the fuel efficiency of an automobile on a road. The present study investigated the effects of cornering motion on automobile aerodynamics, especially focusing on the aerodynamic drag. Using a towing tank facility, measurements of the...
Preprint
Full-text available
This paper presents a one-sided immersed boundary (IB) method using kernel functions constructed via a moving least squares (MLS) method. The resulting kernels effectively couple structural degrees of freedom to fluid variables on only one side of the fluid-structure interface. This reduces spurious feedback forcing and internal flows that are typi...
Conference Paper
To develop a ship with higher propulsion performance, accurate estimation method is required. Tthe performance of ships is estimated by both experimental methods using scale models and numerical methods based on computational fluid dynamics (CFD) using Reynolds average Navier-Stokes equation (RANS) models. Experiments with scale models have limitat...
Article
This report presents an investigation of the characteristics for transitional natural-convection flow in an open-ended inclined channel with bottom surface heated in the air under uniform heat flux intensity and non-Boussinesq condition. The investigated range of modified Rayleigh number and inclination is from 5.93 × 10^6 to 1.45 × 10^9 and 30° to...
Article
The constraint-based immersed boundary (cIB) method has been shown to be accurate between low and moderate Reynolds number (Re) flows when the immersed body constraint is imposed as a volumetric constraint force. When the IB is modelled as a zero-thickness interface, where it is no longer possible to model a volumetric constraint force, we found th...
Preprint
To design a method to solve the issues of handling 'dirty' and highly complex geometries, the topology-free method combined with the immersed boundary method is presented for viscous and incompressible flows at a high Reynolds number. The method simultaneously employs a ghost-cell technique and distributed forcing technique to impose the boundary c...
Article
Full-text available
In biomechanics research on ski jumping, a series of movements are analyzed by classifying them into six phases: approach, take-off, early flight, stable flight, landing preparation and landing. It is a well-known fact that movement from the take-off to the flight is important for improving performance. In actual competition, the athlete's downhill...
Article
Full-text available
In recent years, the dielectric barrier discharge plasma actuator (DBD-PA), which is a fluid control device, has been investigated for achieving both high aerodynamic performance and pleasing styling of transportation equipment. In this study, the authors installed a DBD-PA system on a simplified three-dimensional bluff automobile body to reduce th...
Conference Paper
In this study, unsteady flow simulations using a large-eddy simulation are conducted to analyze vehicle aerodynamics. The objective is to investigate flow structures that cause unsteady lift fluctuations potentially affecting the drivability of a vehicle. In addition, the dependence on the yaw angle of the incoming flow yaw angle is studied. The ta...
Article
This article presents a numerical investigation of the heat transfer behavior between a symmetric and staggered arrangement of three discrete heat sources in an open-ended vertical channel under non-uniform heating and non-Boussinesq conditions over a range of modified Rayleigh number 1.88×103 to 4.57×105. The staggered arrangement shows an improve...
Article
Full-text available
The aim of this study is to understand the mechanism of dew condensation and try to prevent it on automobile headlamp. In this case, it is necessary to accurately reproduce the complicated shape of the headlamp as the computational model. In addition, the simulation framework for predicting the turbulent flow field accompanied by the high heat sour...
Article
We propose a finite volume formulation for compressible solid using marker particles on the Eulerian mesh based on the building-cube method, which can generate computational meshes automatically and quickly for complex geometries. Velocity boundary conditions at solid interfaces are imposed using marker particles that interpolate velocity to the Eu...
Article
The ski jumper rapidly changes the body posture from crouching to flight posture during take off. In this study, the relationship between flight distance and take-off motion, in terms of trunk angle of attack and lift-drag ratio, was investigated through aerodynamics simulations that reproduce the take-off motion dynamically. The trunk angle of att...
Article
Full-text available
Numerical methods based on CFD (Computational Fluid Dynamics) are rapidly expanding their application range, especially with recent remarkable developments in computer performance. Currently, the RANS (Reynolds average Navier-Stokes equation) model, which is a time-averaged model of turbulent flow, is generally used for ship performance estimation....
Article
Full-text available
Writing high-performance solvers for engineering applications is a delicate task. These codes are often developed on an application to application basis, highly optimized to solve a certain problem. Here, we present our work on developing a general simulation framework for efficient computation of time-resolved approximations of complex industrial...
Article
This study presents a numerical investigation of laminar compressible natural convection flow induced under high-temperature difference in an open-ended inclined parallel-walled channel heated isother-mally and asymmetrically at the top wall (hot plate facing downwards) while the lower plate is considered adiabatic. The investigation is carried out...
Poster
Full-text available
In this study, spatially developing compressible tur-bulent natural convection flow for air along a verti-cal flat plate heated with uniform heat flux for max-imum local Rayleigh number ~ 2 X 1014 is investigat-ed by performing direct numerical simulation. Com-putations for compressible governing equation with-out Boussinesq approximation have been...
Article
Full-text available
The present paper focuses on the optimization of the thermal performance for compressible laminar natural convection flow induced under high-temperature difference in an open-ended vertical channel by optimizing the channel inter-plate spacing using numerical simulation. The present investigation is conducted for a wide range of Rayleigh number (Ra...
Article
In this study, numerical simulation is performed with a focus on the application of new modified preconditioned all-speed Roe scheme to simulate natural convection flows. The new modified preconditioned all-speed Roe Scheme primarily utilizes the local flow parameters for calculation of the coefficients of numerator in dissipation term of the schem...
Article
Full-text available
We propose a full Eulerian incompressible solid‐fluid interaction scheme capable of achieving high parallel efficiency and easily generating meshes for complex solid geometries. While good scalability of a full Eulerian solid‐fluid interaction formulation has been reported by Sugiyama et al. (2017), their analysis was carried out using uniform Cart...
Preprint
Full-text available
Writing high performance solvers for engineering applications is a delicate task. These codes are often developed on an application to application basis, highly optimized to solve a certain problem. Here, we present our work on developing a general simulation framework for efficient computation of time resolved approximations of complex industrial...
Article
Full-text available
Effects of the mainstream boundary layer thickness and the turbulence intensity on film cooling under low Reynolds number conditions are studied in this work by the direct numerical simulation (DNS). In other to solve low-speed compressible flow problems, several methods of Roe scheme, preconditioning, dual time stepping, and LUSGS are adopted to s...
Article
Shaped film cooling holes have several features that can greatly improve film cooling effectiveness, and it has been studied and utilized in gas turbine engines for decades. Few studies, however, have reported the effects of low mainstream Reynolds number on shaped film cooling holes. In this study, the effects of mainstream Reynolds number on film...
Article
Full-text available
A temperature-dependent visco-hyperelastic formulation is proposed based on an Eulerian finite element method for large-deformation and multi-material problems, which is pertinent in the application to pressure-sensitive adhesives (PSAs). All the basic equations are computed in the Eulerian description because it allows arbitrarily large deformatio...
Article
Full-text available
It is important to accurately estimate the performance in ship design. It is desirable to confirm performance using a full-scale model in real sea. However, at present, this is impossible in terms of cost and time, and difficulty in removing disturbance influence. For that reason, experiments using scaled models have been widely performed, but extr...
Article
This paper focuses on a solid-fluid interaction scheme using PIC (Particle-in-cell) method based on a spatially-fixed Cartesian mesh and proposes a novel implicit scheme to relax the limitation of time-step size. In the present PIC scheme, a solid region is represented by a set of Lagrangian particles, which carry internal variables of solid. Basic...
Article
Full-text available
Large-eddy simulations are conducted for a rotating golf ball and a rotating smooth sphere at a constant rotational speed at the subcritical, critical and supercritical Reynolds numbers. A negative lift force is generated in the critical regime for both models, whereas positive lift forces are generated in the subcritical and supercritical regimes....
Conference Paper
In parallel computing load balancing is an essential component of any efficient and scalable simulation code. Static data decomposition methods have proven to work well for symmetric workloads. But, in today’s multiphysics simulations, with asymmetric workloads, this imbalance prevents good scalability on future generation of parallel architectures...
Article
Unstable phenomena induced by natural convection of parallel square plates are investigated numerically. The geometry belongs to the open boundary problem, and the compressibility of fluids is taken into consideration. The absorbing boundary condition and modified local one-dimensional inviscid relation method are adopted for open boundaries. Numer...
Article
In this paper, we propose a full Eulerian solid-fluid interaction analysis method using the building cube method, which is capable of achieving high parallel efficiency and generating meshes easily for complex geometry with local mesh refinement. Basic equations of solid and fluid are spatially averaged using volume fractions of each material on th...